1. Field of the Invention
The present invention relates to a hard disk drive. More particularly, the present invention relates to a voice coil motor (VCM) of a hard disk drive.
2. Description of Related Art
Hard disk drives (HDDs) are widely used as auxiliary memory devices of computer systems because of their ability to rapidly access a large amount of data. HDDs do this by recording data on a disk or reproducing data from the disk using a read/write head. Recent advances in the development of HDDs have led to higher memory capacities, namely increased number of TPI (tracks per inch) and BPI (bits per inch). Accordingly, HDDs are being incorporated into greater numbers of electronic products. In particular, there is now a high demand for compact HDDs for use in portable electronic products such as notebooks, personal digital assistants (PDAs), and mobile phones. In this respect, a compact HDD whose disk has a diameter of 0.8 inches, i.e., a diameter similar to that of a coin, has been recently developed for use in mobile phones and MP3 players.
FIGS. 1 and 2 illustrate the structure of a conventional compact HDD. The conventional HDD 101 includes a disk pack 110 consisting of a disk 111 for recording data and a spindle motor (not shown) rotating the disk about an axis 113, a head stack assembly (HSA) 140, a voice coil motor (VCM), and a base 190 on which the aforementioned components are installed. The HSA 140 is rotated by the VCM about a shaft 142. The HSA 140 includes a read/write head 141 for recording data on the disk 111 or reading data from the disk 111, an actuator arm 143, a suspension coupled to an end of the actuator arm 143 and supporting the read/write head 141 so as to bias the head 141 toward the disk 111, a shaft holder 144 that receives the shaft 142 and from which the actuator arm 143 extends such that the actuator arm 143 is rotatable about the longitudinal axis of the shaft 142, and a bobbin 145 integral with the actuator arm 143 and extending from the other side of the shaft holder 144 opposite the actuator arm 143.
The VCM is used to rotate the actuator arm 143 and thereby move the read/write head 141 to a position over a desired location (track) on the disk 111. To this end, the VCM includes a voice coil 150 wound around the bobbin 145, magnets 161 disposed on opposite sides of the voice coil 150, respectively, and a VCM yoke (not shown) to which the magnets 161 are mounted. The VCM yoke helps concentrate the magnetic flux of the magnetic field generated by the magnets 161 across the VCM coil 150. The VCM thus operates according to Fleming's left hand rule, that is, a force is generated on the voice coil 150 (conductor) when current flows through the voice coil 150 within the magnetic field produced by the magnets 161.
Referring to FIG. 2, current flows through sections A and B of the voice coil 150 in respective directions that are opposite one another. The poles of the magnets 161 are arranged such that lines of the magnetic field produced by the magnets extend in opposite directions on opposite sides of a center line C of the magnets. Also, the center line C lies intermediate the sections A and B of the voice coil 150 throughout the entire range of rotation of the HSA 140. Thus, the forces exerted on the sections A and B of the voice coil act in the same direction. However, such magnets 161 having different magnetic poles with respect to their center line C are difficult to manufacture.
Also, as is clear from the description above, the VCM yoke to which the magnets 161 are attached must encompass the entire area over which the bobbin 145 can move when the HSA is driven by the VCM. Also, the voice coil 150 is wound around nearly the entire area of the upper surface of the bobbin 145. Accordingly, the magnets 161 must be relatively large. Furthermore, the magnets 161 must be spaced a relatively great distance from one another due to the thickness of the voice coil 150. Therefore, the VCM limits the degree to which the size and thickness of the HDD 101 can be minimized.